1. Field of the Invention
The present invention relates to a semiconductor device, and particularly to a semiconductor device capable of suppressing a variation in high-frequency characteristic.
This application is counterpart of Japanese patent applications, Ser. No. 101063/2002, filed Apr. 3, 2002, the subject matter of which is incorporated herein by reference.
2. Description of the Related Art
With the scale down of a portable device, there has been a demand for a reduction in size of a semiconductor device mounted in the portable device. In order to meet the need thereof, a semiconductor device called a Chip Size Package having outer dimensions substantially identical to those of a semiconductor chip has been brought into sight. As one form of the Chip Size Package, there exists a semiconductor device called a Wafer Level Chip Size Package or a Wafer Level Chip Scale Package.
A structure of such a Wafer Level Chip Size Package (hereinafter called “WCSP”) will be described using FIGS. 1 through 3.
FIG. 1 is a plan view showing the conventional WCSP prior to being sealed with an sealing resin, and FIG. 2 is a plan view illustrating the conventional WCSP subsequent to having been sealed with the sealing resin, respectively. FIG. 3 is a schematic cross-sectional view taken along line 3—3 in each of FIGS. 1 and 2.
The conventional WCSP has a semiconductor substrate 101. An electronic circuit comprising transistors, resistors, capacitors, inductors, etc. is formed on the surface of the semiconductor substrate 101. A plurality of electrode pads 103 connected to the electronic circuit are formed on the surface of the semiconductor substrate 101.
An insulating layer 301 composed of silicon oxide or the like is formed on the semiconductor substrate 101 excluding some of the surfaces of the electrode pads 103. A protective film 303 composed of polyimide or the like is formed on the insulating layer 301. Owing to such a structure, some of the surfaces of the electrode pads 103 are exposed by openings defined by the insulating layer 301 and the protective film 303.
One ends of wiring layers 105 composed of, for example, copper, are connected to their corresponding electrode pads 103 via the openings of the insulating layer 301. The wiring layers 105 extend over the protective film 303 so as to range from the electrode pads 103 to lower portions of columnar electrodes 305. The other ends of the wiring layers 105 are respectively pad portions 111 disposed below the columnar electrodes 305 and external terminals 201. The pad portions 111 are placed in positions near a central area of the semiconductor substrate 101 as viewed from the electrode pads 103.
The wiring layers 105 respectively perform the function of substantially shifting the positions of the external terminals 201 from a peripheral portion of the semiconductor substrate 101 to the central area of the semiconductor substrate 101. In general, such a shift is called “relocation”. Therefore, the wiring layers each of which performs such a shift, are called “relocating wirings or re-distribution wirings”. The wiring layers 105 will be called “re-distribution wirings 105” below.
The columnar electrodes 305 composed of, for example, copper are formed on their corresponding pad portions 111 of the re-distribution wirings 105.
An sealing resin 203 composed of an epoxy resin is formed over the semiconductor substrate 101 except for the upper surfaces of the columnar electrodes 305.
The external terminals 201 composed of, for example, solder are formed on their corresponding upper surfaces of the columnar electrodes 305. As shown in FIG. 2, a plurality of the external terminals 201 are regularly disposed above the semiconductor substrate 101 at intervals A. In the WCSP shown in FIG. 2, the external terminals 201 are disposed in two rows.
After the formation of the electronic circuit, process steps up to the formation of the insulating layer 301 remain unchanged in the case of WCSP and QFT (Quad Flat Package). Namely, a wafer process and a circuit layout do not depend on the form of a package. Thus, it can be said that WCSP is a package capable of easily realizing downsizing of a semiconductor device.
[Problems that the Invention is to Solve]
It is however necessary to take into consideration the occurrence of the following problems where a high-frequency circuit is disposed in an area 107 indicated by diagonal lines in FIGS. 1 through 3.
The high-frequency circuit is a circuit for processing a signal having a relatively high frequency or a circuit for generating a signal having a relatively high frequency. As one example of the high-frequency circuit, there is known a voltage controlled oscillator (VCO: Voltage Controlled Oscillator) having such inductor elements (coils) 401 and 403 and capacitor elements 405 and 407 as shown in FIG. 4. The inductor elements and the capacitor elements are important elements for determining an oscillation frequency of the voltage controlled oscillator. When, for example, inductance values L of the inductor elements are varied, the oscillation frequency of the voltage controlled oscillator is varied.
As another example of the high-frequency circuit, there is known an RF circuit for processing a radio signal. The RF circuit includes, for example, an LNA circuit (Low Noise Amplifier) and a PA circuit (Power Amplifier). An inductor element for taking impedance matching with an external line or path is built in the RF circuit. The inductor element is also an important element for determining the characteristic of the RF circuit. When, for example, unnecessary electromagnetic coupling is given to the inductor element or a parasitic inductor occurs, the matching of impedance between the RF circuit and the external line cannot be made, so that the characteristic of the RF circuit, e.g., an output characteristic of an antenna section will vary.
Re-distribution wirings 105, columnar electrodes 305 and external terminals 201 exist in the area 107. When the re-distribution wirings 105, columnar electrodes 305 and external terminals 201 are disposed within the area 107, the inductor element, the re-distribution wirings 105, the columnar electrodes 305 and the external terminals 201 disposed on the surface of the semiconductor substrate 101 in the area 107, for example, come close to one another in distance. Thus, electromagnetic coupling (or parasitic inductors or parasitic capacitors) are developed between the inductor element and each of the re-distribution wirings 105, between the inductor element and each of the columnar electrodes 305 and between the inductor element and each of the external terminals 201. Hence the characteristic of the inductor element, e.g., an inductance value L or a Q factor (Quality Factor), or the impedance varies. As a result, the oscillation frequency of the voltage controlled oscillator varies, or the characteristic (e.g., output characteristic of antenna section) of the RF circuit varies. Such a case is a case which is unlikely to take place in QFP in which no external terminals (leads) are disposed above the semiconductor substrate. Further, this is a case peculiar to a package like WCSP in which the external terminals are disposed above the semiconductor substrate.
Thus, a semiconductor device capable of suppressing a variation in high-frequency characteristic has been desired.